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Farmed vs. wild salmon -- which is better?

Compared to farmed salmon, wild salmon is more nutritious and carries fewer toxins that can accumulate in humans, a CTV News investigation has found.

Samples of wild Pacific salmon tested on behalf of CTV News at laboratories in B.C. had eight times more Vitamin D and three times more Vitamin A than farmed Atlantic salmon. The samples of wild salmon were also leaner.

But that doesn't mean you should avoid farmed salmon, dietitians say. The benefits of this nutrient-rich food are so great that it should be a staple in all diets, regardless of the source, they say.

"If you can still afford the gold standard of wild salmon, that's the best. If not, then farmed salmon is still really good for you," said Lori Petryk, a Vancouver-based dietician.

CTV does the testing

All servings of salmon are a good source of Omega-3 fatty acids and vitamins A and D, however wild salmon packs more nutritional benefit per ounce.

Lab tests showed that samples of wild Pacific salmon had more than 500 International Units of Vitamin D, while farmed salmon had far less – just 60 I.U. For children and adults under the age of 50, Health Canada recommends 200 I.U. of Vitamin D each day.

The tested samples of wild salmon also had 154 I.U. of Vitamin A compared to 40 I.U. found in the samples of farmed salmon. Likewise, the fat content of wild salmon was 2.5 per cent while farmed salmon had three times the fat, an overall 13 per cent fat content.

Because of the higher fat content, farmed salmon can store more Omega 3 fatty acids than wild salmon. But this also means farmed salmon can accumulate higher levels of toxins such as PCBs, a banned toxin found in materials like asbestos.

Today, much of the salmon sold in grocery stores is farmed Atlantic salmon produced in B.C. and, according to the provincial government, is responsible for as many as 3,500 direct and indirect jobs.

The aquaculture industry in B.C. is monitored by the province, and 91 farms on the mainland and Vancouver Island were inspected in 2008. That same year, a joint report from the Ministry of Agriculture and Lands and the Ministry of the Environment said the success of the industry "depends on farms being environmentally sustainable and socially acceptable."

Like apples and oranges

Unlike wild salmon whose lifecycles take them from Interior streams to unknown depths of the Pacific Ocean, farmed fish are raised in floating net pens and eat a diet of fish oils, plant-based proteins and pellets of concentrated nutrients.

Mary Ellen Walling of the BC Salmon Farmers Association said the diet given to farmed salmon is designed to resemble that of wild Pacific salmon. And she points out that wild and farmed salmon are actually different species.

"It would be like taking a glass of Chardonnay and comparing it to a Riesling," said Walling, who says she prefers to eat fresh salmon -- whether farmed or wild.

"Pink salmon and sockeye salmon and chum salmon all have a little bit of a different flavour. We grow mostly Atlantic salmon here in British Columbia that has a milder texture, milder flavour and a bit of a bigger flake."

Farmed salmon are also given a carotenoid – a pigment found in plants like carrots -- that tints the flesh of farmed fish to resemble the rich reds and pinks that occur naturally in Pacific species like Coho and sockeye salmon.

To treat for sea lice, early in their lifecycle, farmed salmon are given a chemical therapeutant that Walling said is used very judiciously and results in "very little residue left in the marine environment."

Toxic soup

Jay Ritchlin, the director of marine and freshwater conservation at the David Suzuki Foundation, believes humans can safely eat limited amounts of farmed salmon but says food with any PCBs and other contaminants should be avoided when possible.

Ritchlin says he is more concerned about the environmental burden of international fish farming and advocates for more sustainable practices.

"The waste from the salmon farms, disease and parasites from the salmon farms, escaped farmed salmon all get out in the environment and have a harmful effect on the ecosystem and the wild salmon."

Ritchlin points to trace amounts of PCBs found in farmed salmon as evidence the aquaculture industry needs to make changes.

"About a third or more of the wild fish caught in the world are destined to be ground up and turned into feed for other animals, and particularly aquaculture is one of the things that uses that fish meal and that fish oil," he said.

Wild fish build toxins in their bodies like many plants and animals and those chemicals are further concentrated when fish are turned into food for farmed salmon – and that concentration carries through to the fish sold in stores, he says.

Murray Isman, the Dean of the Faculty of Land and Food Systems at UBC, says levels of PCB contaminants are higher in farmed salmon but they aren't concentrated enough to pose a significant health risk even over time.

"They are probably higher than in wild fish, but I think the important point [is] that they are 50 to 70 times lower than the acceptable level as determined by Health Canada," he said.

Like the banned pesticide DDT, PCBs behave similarly in the environment and very small amounts can be detected in humans, said Isman.

"But the question is, again, is there a health impact from that? Even though these things are in our bodies and we do accumulate them in our diet, really they're far, far below the levels that would have any impacts on our health," he told CTV News.